Adaptive Optics (AO) is a term commonly given to the improvement of the performance of optical systems by reducing the effect of varying wavefront distortions. It is used in astronomical telescopes and laser communication systems to remove the effects of atmospheric turbulence, and in imaging systems to reduce the improve image sharpness. AO systems work by measuring distortions in a path and using a device to compensate for them. The extent to which AO can effectively improve resolution, however, fundamentally depends on its ability to accurately measure, track and correct the distortions.
Current AO systems have limited ability to correct errors that have relatively higher spatial-frequency content. This higher frequency content may contribute to scatter due to the angular spectrum associated with it. Wavefront correctors may alter the phase profile of an incident wavefront by changing the physical length over which the wavefront propagates, or changing the refractive index of the medium through which the wavefront passes. Correctors based on mirror technology may change the phase by altering their surface shape (i.e., change their physical length while keeping the refractive index constant). Some devices, such as those based on liquid crystal technologies, rely on localized changes in refractive index. Very small actuator spacings have been thusfar achieved only by use of refractive modulators and micro-mechanical-systems (MEMS), which typically have “hard” boundaries as a result of their more discrete nature, and typically have increased scatter due to those boundaries.
For laser resonators, this means that the corrected system must typically be of the order of 10s of centimeters in aperture to accommodate higher order correction (referred to aperture) using available AO correctors or use telescopic elements. The expense of current wavefront correctors as well as limited power handling capability for the more modestly priced units has caused most researchers to abandon AO correction for small-bore resonator applications in a manufacturing environment.
Therefore, it may be desirable to have an apparatus and method that takes into account at least some of the issues discussed above, as well as possibly other issues.